Why is parallel arrangement used in domestic wiring?

Three bulbs each having power P are connected in series in an electric circuit. In another circuit another set of three bulbs of same power are connected in parallel to the same source. Now let one bulb in each circuit get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason.

Three bulbs each having power P are connected in series in an electric circuit. In another circuit another set of three bulbs of same power are connected in parallel to the same source. Representing each bulb by a resistor, draw circuit diagram for each case.

An electric lamp of resistance $20 \mathrm{\Omega }$ and a conductor of resistance $4 \mathrm{\Omega }$ are connected to a $6 \mathrm{V}$ battery as shown in the circuit. Calculate:

(a) the total resistance of the circuit,
(b) the current through the circuit,
(c) the potential difference across the (i) electric lamp and (ii) conductor, and
(d) power of lamp.